Re: [PATCH] arm64/kdump: pass dm-crypt keys to kdump kernel

[Coiby Xu <coxu@redhat.com>]

On Tue, Jan 06, 2026 at 09:44:37AM -0600, Rob Herring wrote:
>On Fri, Dec 26, 2025 at 8:11 AM Coiby Xu <coxu@redhat.com> wrote:
>>
>> Based on the CONFIG_CRASH_DM_CRYPT feature, this patch adds
>> LUKS-encrypted device dump target support to ARM64 by addressing two
>> challenges [1],
>>  - Kdump kernel may not be able to decrypt the LUKS partition. For some
>>    machines, a system administrator may not have a chance to enter the
>>    password to decrypt the device in kdump initramfs after the 1st kernel
>>    crashes
>>
>>  - LUKS2 by default use the memory-hard Argon2 key derivation function
>>    which is quite memory-consuming compared to the limited memory reserved
>>    for kdump.
>>
>> 1st kernel will add device tree property dmcryptkeys as similar to
>> elfcorehdr to pass the memory address of the stored info of dm-crypt
>> keys to the kdump kernel.
>
>Is there not any security issue with putting the key into the DT? The
>DT is provided to userspace. There's provisions already to not expose
>"security-*" properties to userspace (see __of_add_property_sysfs).
>Though I think that has a hole in that the FDT is also provided as-is.
>However, I don't even know who or what uses these properties.
>
>Rob

Hi Rob,

Thanks for raising the concern! If I understand DT correctly, this
property is only accessible to the kexec'ed kdump kernel. A new DT is
allocated and set up by of_kexec_alloc_and_setup_fdt. Btw, to be
precise, it's putting the memory address where the key is stored but
not the key itself into DT. The key is stored in the memory exclusively
reserved for kdump. For more info on by who and how this property will
used, I've created a dt-schema pull request as suggested by Krzysztof,
https://github.com/devicetree-org/dt-schema/pull/181

And yes, there is no need for even userspace of the kdump kernel to
access it. So this idea of "security-*" properties/__of_add_property_sysfs
seems desirable. Thanks for bringing it up! I'll give it a try.


-- 
Best regards,
Coiby